The present invention relates to an electron beam-irradiating reaction apparatus for irradiating a desired object with an electron beam and changing properties thereof.
Generally, in an electron beam-irradiating reaction apparatus, thermoelectrons are generated by using a filament provided at an inner end portion of an accelerating tube which provides an electron accelerator, and an electron beam is formed by accelerating the thermoelectrons in the accelerating tube, followed by irradiation of the electron beam to a desired object through a scanning tube connected to the accelerating tube. An electron beam release window, which is formed at an end portion of the scanning tube from which an electron beam is released, includes a metal window foil attached thereto for shielding the inside of the scanning tube in a vacuum state from the outside. When an electron beam passes through the metal window foil, a part of its energy is converted to thermal energy, to thereby heat the metal window foil. Therefore, a cooling gas is blown against the metal window foil to cool the foil to a temperature such that no deterioration of the foil occurs. The metal window foil, in many cases, is made of titanium or an alloy thereof, and has a thickness of several to several tens xcexcm. When such a foil is used, its temperature in a cooled condition should be 200 to 400xc2x0 C.
A typical example of an electron beam-irradiating reaction apparatus is an electron beam gas treatment apparatus in which an electron beam such as that mentioned above is irradiated to a gas such as a combustion gas from a boiler, which contains sulfur oxides or nitrogen oxides, or an exhaust gas discharged from a painting booth, which contains a volatile organic compound, to thereby remove harmful substances such as nitrogen oxides or sulfur oxides contained in the gas. In this gas treatment apparatus, an electron beam irradiation device is set to a position such that an electron beam release window of a scanning tube thereof is in alignment with an electron beam receiving window provided in a side wall of an electron beam reaction device (generally a part of an exhaust gas duct) which allows passage of an exhaust gas therethrough. An electron beam is irradiated through the electron beam release window and the electron beam receiving window to a gas passed through the reaction device.
FIG. 1 shows an example of a conventional electron beam gas treatment apparatus, especially an end portion of a scanning tube 12 and an area in the vicinity thereof (apparatuses similar to that of FIG. 1 are disclosed in FIG. 1 of Unexamined Japanese Patent Application Public Disclosure No. 51-96998, FIG. 2 of Unexamined Japanese Patent Application Public Disclosure No. 52-37553, FIG. 1 of Unexamined Japanese Patent Application Public Disclosure No. 52-149596, FIGS. 1 and 2 of Unexamined Japanese Patent Application Public Disclosure No. 53-75163, FIG. 1 of Unexamined Japanese Utility Model Application Public Disclosure No. 55-107228, FIGS. 1 and 4 of Unexamined Japanese Utility Model Application Public Disclosure No. 63-168899, FIGS. 1 and 7 of Unexamined Japanese Utility Model Application Public Disclosure No. 63-168900 and FIG. 5 of Unexamined Japanese Patent Application Public Disclosure No. 8-166498).
The scanning tube 12 includes an electron beam release window 13 formed at an end portion thereof. A flange 36 is formed along the outer periphery of the end portion of the scanning tube 12. A metal window foil 14 is fixedly held between the flange 36 and a holding plate 16 for maintaining an internal vacuum of the scanning tube 12.
An electron beam reaction apparatus (an exhaust gas duct in the case of treatment of an exhaust gas from a boiler) 18, through which a gas irradiated with an electron beam flows, includes an electron beam receiving window 15 formed in a side wall thereof for receiving an electron beam. A (secondary) metal window foil 34 is provided by means of holding plates 53 and 56 so as to hermetically close the electron beam receiving window.
An electron beam is irradiated into the electron beam reaction device through the metal window foils 14 and 34. As mentioned above, the metal window foils absorb energy of the electron beam and are heated. As a result, it is necessary to cool the metal window foils to a temperature such that no lowering of the strength of the foils occurs. Therefore, in this apparatus, cooling gas nozzle members 51 and 57, which include gas slits (or blow openings) 52 and 58 for blowing a cooling gas against the respective metal window foils, are provided in a space between the metal window foils 14 and 34.
In this case, however, a cooling gas which has been blown against the metal window foils 14 and 34 is diffused into the environment giving rise to the following problems. That is, the cooling gas receives the irradiation of the electron beam when passing through a region where the electron beam passes. When air is used as the cooling gas, ozone and nitrogen oxides (which are harmful to humans and cause corrosion of metallic materials) are produced due to the irradiation of an electron beam. When an inert gas such as nitrogen is used as the cooling gas, although production of ozone and nitrogen oxides in the cooling gas can be prevented, the inert gas after use is subjected to disposal. This is highly disadvantageous in terms of economy.
FIG. 2 shows another example of a conventional electron beam gas treatment apparatus (apparatuses similar to that of FIG. 2 are disclosed in FIGS. 3 and 5 of Unexamined Japanese Patent Application Public Disclosure No. 8-166497 and FIG. 5 of Unexamined Japanese Patent Application Public Disclosure No. 9-171098). The arrangement of the apparatus of FIG. 2 is substantially the same as that of the apparatus of FIG. 1, except that the cooling gas nozzle assembly is changed. The same elements as those shown in FIG. 1 are designated by the same reference numerals, and an explanation thereof is omitted.
In this apparatus, in order to solve the above-mentioned problems, the cooling gas nozzle assembly is formed integrally with a cooling gas nozzle member 61 for the primary metal window foil 14, a cooling gas nozzle member 67 for the secondary metal window foil 34, and exhaust gas tubular passages 65 and 69 disposed so as to face gas slits 62 and 68 of the respective nozzle members. Thus, a cooling gas is supplied and discharged through the tubular passages hermetically sealed from the atmosphere.
With this arrangement, a cooling gas which has passed through the region of passage of the electron beam is not diffused into the atmosphere and can be recovered. Therefore, when air is used as the cooling gas, it is possible to introduce the cooling gas recovered from a discharge opening into a device where the gas is made harmless. Further, it is also possible to use an inert gas such as nitrogen as the cooling gas in a circulative manner.
FIG. 3 shows another example of a conventional electron beam gas treatment apparatus (apparatuses similar to that of FIG. 3 are disclosed in FIG. 4 of Unexamined Japanese Patent Application Public Disclosure No. 52-37553, FIG. 2 of Unexamined Japanese Patent Application Public Disclosure No. 52-149596, FIGS. 3 and 4 of Unexamined Japanese Patent Application Public Disclosure No. 53-21397, FIG. 2 of Unexamined Japanese Patent Application Public Disclosure No. 53-46598, FIGS. 1 and 3 of Unexamined Japanese Utility Model Application Public Disclosure No. 5-30800 and FIG. 2 of Unexamined Japanese Utility Model Application Public Disclosure No. 6-51900).
In the apparatus of FIG. 3, as in the case of FIG. 2, a sealable space is formed between the primary metal window foil 14 and the secondary metal window foil 34. However, in the apparatus of FIG. 3, a single cooling nozzle member 71 and a single exhaust gas tubular passage 73 are disposed adjacent to each other on one side of the sealable space. A cooling gas which has been blown against the primary metal window foil through a slit 72 of the cooling nozzle member 71 is inverted on the other side of the sealable space and returns to the exhaust gas tubular passage 73 for discharge.
However, in the case of the apparatuses of FIGS. 2 and 3, the following problems arise.
An exhaust gas duct as the electron beam reaction device and an electron beam irradiation device are individually set on different base members. The scanning tube 12 of the electron beam irradiation device is rigidly connected to a side wall of the exhaust gas duct through the cooling gas nozzle assembly comprising the cooling nozzle members 61 and 67 or the single cooling nozzle member 71. Therefore, an excessive stress is likely to be applied to a connecting portion between the scanning tube 12 and the side wall of the exhaust gas duct. Consequently, the metal window foil cannot be fixed to the flange at the outer periphery of the end portion of the scanning tube by the holding plate, so that the vacuum in the scanning tube cannot be maintained. In an extreme case, the metal window foil is displaced and forced into the scanning tube, leading to fracture of the foil.
In particular, in a conventional electron beam-irradiating reaction apparatus, it is preferred to omit a secondary metal window foil and use only a primary metal window foil, from the viewpoint of reducing energy loss of an electron beam at the metal window foil, reducing energy required for blowing a cooling gas, and simplifying the structure of the cooling gas nozzle assembly. In such an arrangement, however, when fracture of the primary metal window foil occurs, an exhaust gas enters the scanning tube of an electron beam generator which is required to be maintained in a vacuum condition, and serious contamination or damage is likely to occur. Therefore, it has been considered that it is difficult to realize an electron beam-irradiating reaction apparatus using only a primary metal window foil.
It is an object of the present invention to provide an electron beam-irradiating reaction apparatus which prevents the above-mentioned problems due to rigid connection between the scanning tube of the electron beam irradiation device and the electron beam reaction device in conventional electron beam-irradiating reaction apparatuses and which is free from leakage of a gas to be treated, such as an exhaust gas, and a cooling gas.
According to the present invention, there is provided an electron beam-irradiating reaction apparatus comprising: an electron beam irradiation device including an electron beam release window at an end portion thereof for releasing an electron beam in a scanning condition, the electron beam release window having a primary metal window foil extended for maintaining an internal vacuum. An electron beam reaction device receives a gas irradiated with an electron beam, the electron beam reaction device having an electron beam receiving window formed in a side wall thereof for receiving the electron beam from the electron beam irradiation device. A cooling gas nozzle assembly includes a blow opening for blowing a cooling gas against the metal window foil, and a flexible cylindrical hermetic sealing member is connected between the end portion of the electron beam irradiation device and a peripheral edge of the electron beam receiving window in window in the side wall of the electron beam reaction device for preventing leakage of the cooling gas between the end portion and the side wall to the outside.
In this apparatus, no rigid connection is made between the electron beam irradiation device and the electron beam reaction device. Therefore, no excessive load is applied to a connecting portion between these devices. Further, this connecting portion is covered by the flexible cylindrical member, so that the cooling gas irradiated with the electron beam is not diffused to the outside.
Specifically, the cooling gas nozzle assembly is provided at the end portion of the electron beam irradiation device, and the flexible cylindrical hermetic sealing member is connected between an outer peripheral portion of the cooling gas nozzle assembly and the peripheral edge portion of the electron beam receiving window in the side wall.
More specifically, the electron beam receiving window is sized so as to be larger than a size which defines a peripheral edge of a scanning path of the electron beam. The cooling gas nozzle assembly as a whole is annularly formed so as to surround the scanning path which allows passage of the electron beam, and the cooling gas nozzle assembly is set at a position such that it substantially occupies the electron beam receiving window.
Preferably, a protective member is provided so as to prevent backscattered electrons, which are generated upon irradiation of an electron beam in the electron beam reaction device, from impinging on the flexible cylindrical hermetic sealing member. Further, the primary metal window foil is sealably fixed at a peripheral edge of the electron beam release window by means of a removable holding plate. The cooling gas nozzle assembly includes a removable portion which is set so as to form a cooling gas blow opening between it and the holding plate, and the metal window foil is capable of being replaced by removing the removable portion and removing the holding plate.
Further, it is preferred that the cooling gas blown against the primary metal window foil have a moisture content equal to or higher than a critical humidity of fine powders in the gas, which are deposited on a surface of the primary metal window foil that contacts the gas. The reason for this is as follows. When an object to be treated by the electron beam-irradiating reaction apparatus is an exhaust gas containing sulfur oxides or nitrogen oxides, fine powders of ammonium sulfate or ammonium nitrate can be formed as a by-product derived from the sulfur oxides or nitrogen oxides, due to irradiation of an electron beam in the reaction device. These powders are likely to be deposited on the metal window foil. Therefore, a cooling gas having a moisture content equal to or higher than the critical humidity is blown against the metal window foil, so that the fine powders deposited on the foil absorb moisture in the cooling gas and are easily peeled off from the metal window foil.
For the same purpose, the cooling gas may contain drops of water. However, when the drops of water in the cooling gas contain a suspendible solid or a water-soluble substance and impinge on the metal window foil which has been heated by irradiation of an electron beam, the suspendible solid or water-soluble substance is dried and solidified due to vaporization of a water component, and can be fixed to the metal window foil. To prevent this problem, it is preferred that the drops of water contained in the cooling gas consist of pure water, which drops are obtained by, for example, spraying pure water into the cooling gas.
Further, in the present invention, an arrangement may be made such that the cooling gas nozzle assembly as a whole is annularly formed so as to surround the scanning path for passage of the electron beam. In addition, the cooling gas nozzle assembly includes a secondary metal window foil provided at an end face thereof on a side of the electron beam reaction device so as to extend across the scanning path, a blow opening for blowing a cooling gas against the primary and secondary metal window foils, and a discharge opening for discharging the blown cooling gas to the outside. In this case, it is possible to have an arrangement such that the cooling gas nozzle assembly includes first and second blow openings for blowing a cooling gas against the primary and secondary metal window foils, respectively, first and second receiving openings for receiving a cooling gas from the outside and supplying the gas to the first and second blow openings, respectively, and first and second discharge openings for discharging the cooling gas blown from the first and second blow openings against the first and second metal window foils, respectively, to the outside.